This invention relates to a developing apparatus used in an image forming apparatus such as a copier or a printer using the electrophotographic method or the electrostatic recording method to develop an electrostatic image on an image bearing member.
In an image forming apparatus using the electrophotographic method, it has heretofore been practiced to visualize an electrostatic latent image formed on an image bearing member as a toner image by a developing apparatus.
As examples of such a developing apparatus, there have been proposed various dry type monocomponent developing apparatuses. Also, when visualizing the electrostatic latent image, a developer carrying member is adopted to carry a developer to the image bearing member such as a photosensitive drum.
There has heretofore been proposed a contact monocomponent developing method of effecting development by using an electrically semiconductive developing roller or a developing roller having a dielectric layer formed on the surface thereof as the developer carrying member, and pressing it against the surface layer of a photosensitive body.
In such a system, the developing roller contacts with the surface of the photosensitive body and is rotated to thereby effect development and therefore, an elastic material is generally used for the developing roller. Also, functions required of the developing roller include that a necessary developing nip can be obtained, that the developing roller has a sufficient recovering property for a compressive force to the contact, that a toner on the developing roller obtains a desired charging polarity and charging amount, that the surface of the developing roller is excellent in the releasing property with respect to a developer (hereinafter referred to also as the toner) and the toner does not film on the surface of the roller, etc.
Therefore, as the construction of the developing roller, use is generally made of such a multilayer construction that satisfies functions required of the vicinity of the surface of the developing roller and functions required of the interior of the developing roller.
A developing roller of such a multilayer construction generally has a surface layer formed on an elastic layer as an underlying layer by dip coating, roll coating or the like.
Also, as compared with a magnetic developing apparatus which uses a magnetic toner and can easily hold the toner on the surface of a developing sleeve by the action of a magnetic field, in a developing apparatus using a non-magnetic toner as a developer, a magnetic attracting force cannot be used and therefore, it becomes difficult to prevent the leakage of the toner out of the developing apparatus.
Here, the developing apparatus will be described with reference to FIG. 8 of the accompanying drawings. FIG. 8 shows the structure of the developing apparatus, and is a view of a developing container 24 as it is seen from the opening portion side thereof.
A developing roller 25 is disposed in the opening portion of the developing container 24. This developing roller 25 is rotated in the direction of arrow B. Also, the developing roller is supplied with a toner by an elastic roller (not shown) located upstream of the position of the contact portion between the developing roller 25 and an elastic blade 27 with respect to the direction of rotation and contacting with the developing roller 25.
The toner supplied to the developing roller 25 is carried to the contact portion between the elastic blade 27 and the developing roller 25 with the rotation of the developing roller 25 and is made into a thin layer.
Thereafter, the toner is carried onto a photosensitive body (not shown) which is an image bearing member, whereby the development of an electrostatic latent image is effected.
Also, a flexible seal member 26 lightly contacting with the developing roller 25 is provided in a toner collecting portion (the downstream side of the developing roller with respect to the direction of rotation thereof) which is the lower portion of the developing container 24, to thereby permit the passage of the toner unused for development and prevent the toner in the developing container 24 from leaking out of the lower portion of the developing container 24.
Further, end portion seal members 29 formed of a fibrous material such as woolen felt or polytetrafluoroethylene (herein referred to as PTFE) pile or a foamed material such as polyurethane foam or sponge rubber are provided in the gaps between the opposite end portions of the developing roller 25 and the opening portion of the developing container 24 to thereby prevent the leakage of the toner from between the developing container 24 and the lengthwisely opposite end portions of the developing roller 25.
However, the developing roller having its surface layer formed by dip coating, roll coating or the like as described above is liable to cause an unevenness of the coat on the end portions of the surface layer during the formation of the surface layer.
Therefore, for example, in the outermost peripheral portion of the end surfaces of the elastic layer, the surface layer cannot be stably applied thereto or conversely the surface layer becomes thick. Also when the opposite end portions of the surface layer of the developing roller are lengthwisely inside the elastic layer, it is sometimes the case that when the surface layer is to be applied by roll coating or the like, the surface layer cannot be sufficiently applied at the beginning and end of the application.
When by the use of such a developing roller, the developing operation is repeated a number of times by the conventional developing apparatus as shown in FIG. 8, the end portions of the surface layer of the developing roller 25 have their surface layer peeled off by long-period use because the frictional contact thereof with the end portion seal members 29 is repeated, and with it as an occasion, the peeling-off of the surface layer of the developing roller 25 progresses to the lengthwisely central portion of the developing roller 25.
This state will now be described with reference to FIG. 9 of the accompanying drawings. As shown in FIG. 9, the peeling-off 90 at the end portions of the developing roller 25 progresses to the central portion of the developing roller 25.
As the result, gaps are formed between the opening portion of the developing container 24 and the end portion seal members 29 and the sealing property of the seal members to the leakage of the toner is reduced.
It is an object of the present invention to provide a developing apparatus in which the peeling-off of the surface layer of a developer carrying member is prevented.
It is another object of the present invention to provide a developing apparatus in which the leakage of a developer from the end portions of the apparatus is prevented.
It is still another object of the present invention to provide a developing apparatus comprising:
a developing container for containing a developer therein;
a developer carrying member provided in an opening portion of the developing container, the developer carrying member developing an electrostatic image on an image bearing member; and
a seal member provided in the opening portion for preventing leakage of the developer from an end portion of the opening portion;
the seal member contacting with the end portion of the developer carrying member except for an end edge thereof.
Further objects of the present invention will become apparent from the following description.